1. Field of the Invention
The present invention relates to a time-of-flight mass spectrometer for separating ions according to mass based on the time of flight of the ions.
2. Description of the Related Art
Mass spectrometry is one method for structurally analyzing biological molecules. In mass spectrometry, the substances constituting a biological molecule are identified based on the masses of the substances. Recent years have seen a rising need for measurement of functionally modified proteins such as those modified by phosphoric acids, sugar chains, or the like. In the current field of mass spectrometry, time-of-flight mass spectrometers are most frequently used. The time-of-flight mass spectrometers are designed to measure the flight time it takes for accelerated ions to reach a detector and thereby to measure the masses of the ions. The most frequently used detectors for the time-of-flight mass spectrometers are micro channel plates (MCP), and methods have been proposed to improve their detection efficiency (refer to U.S. Pat. No. 6,906,318, for example).
A wide variety of mass spectrometers such as a quadrupole mass spectrometer and a magnetic sector mass spectrometer have been used in the mass spectrometry field. These mass spectrometers, however, have some restrictions in the size of the mass spectrometers, the strength of electromagnetic fields required for the mass spectrometers, the control voltage applied to the mass spectrometers, and the resolution of the mass spectrometers. Thus, ranges of masses that the mass spectrometers can measure are limited. In addition, a conventional mass spectrometer separates ions by mass, then accelerates the ions with a constant voltage and measures the masses of the ions to improve sensitivity of a measurement of ions having large masses (refer to, for example, JP-A-2001-351565, JP-A-2001-351566 and JP-A-2005-298603).